Method and apparatus for eliminating furnace pulsations



B. R. WALSH Nov. 26, 1968 METHOD AND APPARATUS FOR ELIMINATING FURNACE PULSATIONS 2 Sheets-Sheet 1 Filed Feb. 28, 1967 FIG.

FIG.

INVENTOR BRUCE R. WALSH FIG. 4

Nov. 26, 1968 B. R. WALSH 3,413,069

METHOD AND APPARATUS FOR ELIMINATING FURNACE PULSATIONS Filed Feb. 28, 1967 2 SheetsSheet 2 INVENTOR BRUCE R. WALSH United States Patent 3,413,069 METHOD AND APPARATUS FOR ELIMINATING FURNACE PULSATIONS Bruce R. Walsh, Wiiltensburg, Pa., assignor to Gulf Research & Deveiopment Company, Pittsburgh, Pa., a

corporation of Delaware Filed Feb. 28, 1967, Ser. No. 619,215 Claims. (Cl. 4314) ABSTRACT OF THE DISCLOSURE An air tube for gun type oil burners to eliminate pulsation which includes means to mix both combustion gases and room air into the main air stream upstream from the combustion chamber.

This invention pertains to oil burners of the so-called gun type, which are widely used to burn fuel oil in domestic and commercial heating installations. These burners include a self-contained air blower and means to force the oil under pressure through an oil supply tube within the air tube. The blower, oil supply, and associated apparatus are usually in spaced relation to the combustion chamber of the furnace in which the burner is being used, and the cylindrical air or blast tube interconnects the combustion chamber of the furnace with the rest of the burner apparatus. The furnace may be associated with any type of heat distributing system, i.e., forced air, hot water, or steam.

A problem which sometimes arises in such heating installations is pulsation. Pulsation is a vibrating of the flame, the combustion chamber, any loose parts, and even the entire furnace under extreme conditions, or any combination of these elements, and can occur at start-up, during running, and/or at stopping of combustion. Pulsation is an undesirable phenomena in that it can extinguish the flame, create noise, create noxious odors, wear the equipment prematurely, cause smoke and soot to enter the furnace room, and generally create unpleasant and unsafe situations.

The reasons for the occurrence of pulsations generally are not fully understood, but certain things are strongly suspected causative agents. Certain combinations of the physical configurations of the combustion chamber and the burner resulting in poor air/ oil mixing are thought to be one cause of pulsation. Rough burning of the fuel oil will cause pulsation, such rough burning being caused by interruptions in the smooth flow of air from the blower, interruptions in the smooth flow of oil from the nozzle, random recirculations, uneven drafts in the combustion chamber, and abnormal pressure conditions in the blast tube and/or the combustion chamber. These abnormal pressure conditions can be caused by the above factors, and it is thought that it is primarily abnormal pressure conditions which cause all pulsations, and that the other factors are not primary causes of pulsation, but only operate to cause pulsations because they operate to create abnormal pressure conditions.

Starting pulsations are often caused by a slow start of the draft up the chimney. Running pulsations can be caused by a poor draft or chimney, and is often rhythmic. Pulsations during stopping could be caused by a low pressure condition in the combustion chamber. The present invention eliminates or at least very markedly reduces all types of pulsation.

One prior method of overcoming pulsation comprises the provision of an opening, usually in the form of a short length of pipe, underneath the burner communicating the combustion chamber with ambient room air. While this method is effective in preventing pulsations, it suffers from Patented Nov. 26, 1968 the disadvantage that the air taken into the combustion chamber is not mixed with the air/oil mixture expelled from the burner. The inclusion of this ambient air directly into the combustion chamber has several detrimental effects of combustion. These include a chilling effect on the flame, which results in poor combustion, resulting in poor economy of use of fuel, increased smoke, and other harmful factors well known to those skilled in this art. Another disadvantage of this prior method of eliminating pulsation is that the tube or opening constitutes a direct, open connection between the room and the combustion chamber. In the event of an abnormally high pressure condition in the combustion chamber, such as is caused by start-up or a downdraft in the smoke stack, a so-called puff-back, combustion gases, smoke, and soot could be expelled into the room, causing health and safety hazards.

I have found that the inclusion of both a flow of combustion gases from the combustion chamber and a flow of ambient room air, into the stream of pressurized air fiowing through the blast tube to the combustion chamber results in the total elimination of or at least a very marked decrease in pulsations, and overcomes the above hazards.

The inclusion of combustion gases has the desirable effect to preheating the air in the blast tube before it mixes with the oil mist in the combustion chamber. The inclusion of the ambient room air is thought to act as a pressure leveler in that the combustion will always draw in some room air through the apparatus 0 the invention, and depending upon the occurrence of abn rmal pressure conditions in the combustion chamber may draw more or less than the normal amount of room air to alleviate the abnormal pressure conditions to thereby prevent pulsations.

The invention comprises a method and apparatus comprising a blower or blast tube assembly which comprises a pair of nested tubes with space between them at both ends, the outer one of which is a cylindrical tube and the inner one of which comprises a pair of truncated cones with their small ends face to face to form a venturi throat mediately the ends of the double tube assembly. A row of openings are provided at the venturi throat in the inner tube, and inlet ports are provided at both ends of the assembly so that the passage of the pressurized air through the inner tube and past the venturi throat will draw in both combustion gases from the front end of the blast tube assembly and room air from the rear end of the blast tube assembly, and separately mix them into the how of pressurized air from the blower at the venturi throat.

Referring now to the accompanying drawing forming a part of this disclosure: FIG. 1 is a partial side elevational view of a heating installation embodying the invention; FIG. 2 is a cross-sectional view taken on line 22 of FIG. 1 showing the blast tube assembly embodying the invention; and FIGS. 3 and 4 are cross-sectional views taken on lines 3-3 and 4-4 of FIG. 2 respectively.

Referring now in detail to the drawing, 10 designates an oil burner which includes a blast tube assembl 12 embodying the invention shown being used in a furnace 14. Blast tube assembly 12 is an integal one-piece structure, and may be fabricated as a weldrnent, or in other suitable manner.

As will be readily apparent to those skilled in this art, the blast tube assembly 12 of the invention can be used in new installations, or can be easily substituted for the air tube in existing installations by merely removing the existing air tube, and substituting assembly 12. In most cases, since the burners have standard size air outlet openings, this substitution can be accomplished by simply removing the adapting means at the burner and at the furnace and reafiixing the same adapting means to the air tube of the invention.

Burner 10, FIG. 2, comprises an outlet opening 16 through which air under pressure is passed by the blower, not shown. Integral blast tube assembly 12 is formed from an outer cylindrical tube 18, and an inner member 20. Member 20 comprises a rear cylindrical end portion 22 that fits within outlet 16 of burner and is secured therein by any suitable means, not shown. Forwardly of rear cylindrical end portion 22, member 20 is formed into a rear truncated cone portion 24. A set of rear support struts 26 connect the rear end of tube 18 with cone portion 24 adjacent cylindrical portion 22. Thus, an annular inlet port 28 is provided between the rear end of tube 18 and cone portion 24 to permit entry of room air into the annular space 30 between tube 18 and inner member 20.

The smaller end of a front truncated cone portion 32 is joined to the smaller end of rear cone portion 24, and a venturi throat is formed at the plane of juncture. Inner member 20 is formed with a row of openings 34 at the venturi throat to admit gases therethrough from annular space 30 into the inside of inner member 20. The front large end of front cone portion 32 is formed into a cylindrical portion 36 which is smaller than the diameter of tube 18 and which is joined thereto by a plurality of front support struts 38 similar to rear struts 26. Thus, an annular inlet port 37 is formedbetween cylindrical portion 36 and tube 18 for admission of combustion gases into annular space 30.

Mounted on the inside of front cylindrical portion 36 by any suitable means is a swirl end cone member 40, provided with swirl vanes 42, to cause the air and oil mixture to swirl to aid combustion, in the usual manner.

Spaced rearwardly of member 40 are support means 44 of any suitable type, which support an oil supply pipe 46 which carriees an oil spray nozzle 48 of any type having its front end positioned substantially in the plane of end cone member 40. Support means 44 also carry electrical ignitors 50 to ignite the oil mist, or any other suitable ignition means. The rear end of oil supply pipe 46 is attached to a suitable means to supply oil under pressure in the burner 10, not shown.

The front end of blast tube assembly 12 is supported in a fire wall 52 of furnace 14 by any suitable means not shown, with the front ends of end cone member 40 and tube 12 positioned in the combustion chamber 54 of the furnace 14.

Operation Air under pressure is supplied through outlet 16 of the oil burner 10 and passes only through inner member 20. Oil under pressure is supplied through supply pipe 46 and nozzle 48 and is ignited by the igniting means 50. A region of low pressure will be created inside of member 20 at the vicinity of the openings 34 because of the action of the venturi throat. As shown by the arrows on FIG. 2, air will be drawn through both annular ports 28 and 37 into annular space 30 and through the row of openings 34 to mix with the main stream of the pressurized air passing through the inner member.

As will be apparent from the symmetry of the structure shown in FIG. 2, the suction at the row of openings 34 will draw gases into annular space 30 from annular port 28 and annular port 37 with approximately equal force.

Under normal conditions, the suction at the openings 34 will be considerably greater than the normal draft occurring in combustion chamber 54. A very slight draft on the order of .02 to .06 inch of water is present in the combustion chamber to permit the combustion gases to be drawn up the stack or chimney. A conisderably larger suction force, on the order of 5 or 6 inches of water, is present at the row of openings 34 under normal operation. If, due to some extraordinary condition causing the suction in the combustion chamber to become greater than the suction at openings 34, such as might occur during stopping of combustion, then the high suction in the combustion chamber will draw room air into port 28 straight through annular chamber and port 36 into the combustion chamber to alleviate the abnormal condition and prevent pulsation. If the opposite condition should occur, that is, an abnormally high pressure condition in the combustion chamber 54, such as might be caused by start-up or running pulsations, then the combustion gases will not be able to flow out to atmosphere through annular port 37, annular space 30 and annular port 28, because there is always some suction at the venturi throat. The combustion gases would be drawn into openings 34 and recirculated. Thus, blast tube assembly 12 is provided with integral and automatic safety features to prevent combustion gases from entering the room should there be some extraordinary happening within the combustion chamber or stack such as puff-back, downdraft, or the like.

The provision of end cone member at the exit end of the blast tube assembly 12 provides the advantage of imparting swirl to the flaming air-oil mist at substantially the plane of inlet ports 37. Further, end cone member 40 confines the flame and insures that the flame will be located spaced considerably inwardly of said inlet ports 37. Swirling the air at the exit and the confining feature of the end cone, provides the advantage of insuring that the back pressure or suction force always present behind the flame is spaced relatively far away from annular inlet ports 37. This insures that this suction force will not suck any gases out of said inlet ports, to further insure that the suction created at the row of openings 34 at the venturi throat will suck combustion gases into annular space 30.

The mixing of the room air and the combustion gases separately into the main stream of pressurized air has been found to entirely eliminate or at least very substantially reduce all pulsations.

While the invention has been described in detail above, it is to be understood that this detailed description is by Way of example only, and the protection granted is to be limited only within the spirit of the invention and the scope of the following claims.

I claim:

1. A method of reducing pulsations in a heating instal- V lation which includes an oil burner having a blast tube;

comprising the steps of substantially separately admixing both ambient room air and combustion gases into the main stream of pressurized air passing through said blast tube at said main stream upstream from the oil spray nozzle within said blast tube.

2. The method of claim 1, constricting the flow stream of said pressurized air mediately the ends of said blast tube to create a region of reduced pressure at said constriction, and causing said region of low pressure at said constriction to draw in both said ambient room air and said combustion gases into said main stream of pressurized air.

3. The method of claim 2, wherein said room air is drawn in from the rear end of said blast tube to said constricted region and said combustion gases are drawn in from the front end of said blast tube to said constricted region.

4. A blast tube assembly for a gun type oil burner comprising an inner member and an outer member, means to mount said inner member within said outer member, said mounting means comprising means to permit passage of fluids from the front and rear ends of said assembly between said inner and outer members to a space between said members, said inner member being formed with a constricted portion mediately the ends thereof, said constricted portion being formed with a plurality of openings, an oil spray nozzle, means to mount said nozzle within said inner member adjacent one end thereof in position to direct the spray from said nozzle outwardly of said blast tube assembly, whereby a flow of pressurized air through said inner member will create a zone of reduced pressure at said constricted portion to draw gases through said passage means at both the front and rear ends of said tube assembly, through said space between said inner and outer members, and through said openings into the main stream of the pressurized air passing through said inner member.

5. The blast tube assembly of claim 4, said one end of said inner member terminating in a common traverse plane with the corresponding one end of said outer member, whereby said mounting means form an annular fluid passage at said one end of said assembly; the other end of said inner member extending outwardly from said constricted portion beyond the corresponding other end of said outer member, said mounting means connecting said other end of said outer member with a portion of said inner member being spaced inwardly from the outer end thereof, said other end of said inner member being formed into a cylindrical portion, said cylindrical portion being adapted to mount said inner member in fluid flow communication with the air outlet opening of an oil burner.

6. The blast tube assembly of claim 4, a swirl end cone member, said end cone member comprising means to swirl the flaming air oil mist issuing from said one end of said blast tube assembly, and means to mount said end cone member within said inner member at said one end thereof.

7. The blast tube assembly of claim 4, said outer member comprising a straight length of plain cylindrical tubing, said inner member comprising a pair of truncated cone portions with their small ends joined to form said constricted portion and with their outer ends adjacent the ends of said outer member, said mounting means comprising front and rear sets of mounting struts in the space between and joining said inner and outer members together at the ends thereof, and the other end of said inner member extending outwardly beyond the corresponding other end of said outer member, said outwardly extending end of said inner member comprising mounting means to mount said inner member of said blast tube assembly in fluid flow communication with the air outlet opening of an oil burner.

8. A unitary, one-piece fluid handling article comprising an elongated inner member and an elongated outer member, means to mount said inner member substantially coextensively within said outer member, said inner member being formed with an inwardly constricted portion mediately the ends of said outer member, said constricted portion being formed with a row of openings communicating the space within said inner member with the space between said inner and outer members, said mounting means comprising front and rear sets of mounting struts in the space between and joining said inner and outer member together at the ends thereof to form front and rear ports at the front and rear ends of said article, whereby a flow of fluid axially through said inner member will create a zone of reduced pressure at said constricted portion, and whereby said zone of reduced pressure will draw fluids from outside the article into said space between said inner and outer members from said front and rear ports and through said openings into said flow of fluid through said inner member.

9. The article of claim 8, and means at the rear end of said inner member adapted to mount said inner member in fluid flow communication with a source of pressurized fluid.

10. The article of claim 8, said outer member comprising an elongated, straight length of plain cylindrical tubing, and said inner member comprising two truncated cone portions having their small ends joined together to form said inwardly constricted portion.

References Cited UNITED STATES PATENTS 1,629,253 5/1927 Breese 1581 2,701,608 2/1955 Johnson l581 2,918,117 12/1959 Griflin l581 FREDERICK L. MATTESON, 111., Primary Examiner.

E. G. FAVORS, Assistant Examiner. 

